Composition for thermally stablizing o-pyridylphosphates or thiophosphates by incorporating various proportions of certain phthalate esters thereto

ABSTRACT

Novel composition and method for thermally stabilizing an O-pyridyl phosphate insecticide such as chlorpyrifos. The insecticide is mixed with a phthalate ester prior to its incorporation into a thermoplastic resin, such as polyvinyl chloride.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of Ser. No. 890,032, filedJuly 28, 1986, now abandoned which is a divisional of Ser. No. 698,779,filed Feb. 6, 1985, now U.S. Pat. No. 4,631,301.

BACKGROUND OF THE INVENTION

This invention relates to novel compositions and methods for thermallystabilizing O-pyridyl phosphate insecticides during its incorporationinto thermoplastic resins.

Thermoplastic resins, polymers which can be softened and shaped by theapplication of heat and pressure and which return to their originalcondition when cooled to room temperature, are used in making articlessuch as underground pipelines and cables.

O-pyridyl phosphate insecticides have been incorporated into pipes andcables made from thermoplastic resins to make the resulting pipe orcable resistant to insect damage, particularly from ants and termites.Generally, in a known method for making insecticides-impregnated pipe, athermoplastic resin, a stabilizer and a phthalate ester are kneadedtogether and then an O-pyridyl phosphate insecticide is incorporatedtherein. This resin containing the O-pyridyl phosphate insecticide ispelleted into beads or pellets which are later used to make the pipe.

However, a problem exists during the step of incorporation of theO-pyridyl phosphate insecticide into the resins as the O-pyridylphosphates are thermally labile and unstable at the temperatures usedfor incorporation. At the temperatures of about 160° to about 200° C.used in the manufacture of plastic articles, the O-pyridyl phosphatesdecompose, thereby preventing manufacturers from accurately andprecisely metering the desired quantity of insecticide into thethermoplastic resin. The present invention overcomes this problem byproviding a composition and a method for thermally stabilizing O-pyridylphosphate compounds during its incorporation into thermoplastic resins.

SUMMARY OF THE INVENTION

The present invention provides a composition comprising

(a) an O-pyridyl phosphate of the formula ##STR1## wherein R representshalopyridyl,

Z is oxygen or sulfur, and each

R¹ is loweralkoxy, amino or loweralkylamino; and

(b) a phthalate ester of the formula ##STR2## wherein Y is alkyl fromabout 2 to about 20 carbon atoms or ##STR3## wherein Y¹ is alkyl from 1to about 20 carbon atoms and

Y² is hydrogen or methyl,

said O-pyridyl phosphate and said phthalate ester being present inproportions effective to prevent appreciable decomposition of saidO-pyridyl phosphate upon heating said composition.

The present invention also provides a method for thermally stabilizingan O-pyridyl phosphate by (a) mixing the O-pyridyl phosphate with aphthalate ester as hereinbefore described and (b) incorporating themixture into a thermoplastic resin. The resin containing the O-pyridylphosphate can then be pelleted into beads, pellets, etc. used to makeplastic articles which are resistant to insect damage.

DETAILED DESCRIPTION OF THE INVENTION

O-pyridyl phosphates, as defined hereinbefore, are known insecticidecompounds. Methods for making these compounds are disclosed in U.S. Pat.No. 3,244,586 incorporated herein by reference. A preferred O-pyridylphosphate is O,O-diethyl-3,5,6-trichloro-2-pyridyl phosphorothioate,commonly known as chlorpyrifos.

Phthalate esters, as defined hereinbefore, are known compounds and areused commercially as plasticizers for many resins and elastomers.Methods for making these compounds may be found in U.S. Pat. Nos.3,064,046 and 3,088,974, incorporated herein by reference. A preferredphthalate ester is dioctyl phthalate.

The term "themoplastic resins" is used herein to include, but it is notlimited to resins of polystyrene, acrylonitrile, methacrylate ester orcombinations thereof. A preferred thermoplastic resin is polyvinylchloride (PVC). Thermoplastic resins are polymer materials well known tothose skilled in the art. Stabilizers for thermoplastic resins arematerials which prevent degradation of the resin exposed toenvironmental variation such as heat, sunlight and the like. Suchstabilizers are known compounds to one skilled in the art.

The composition of the present invention can also contain certaindiluent or additional inert ingredients which would not significantlyaffect its O-pyridyl phosphate thermal-stabilizing properties.

By way of illustration such diluents would include, but would not belimited to, toluene, benzene, xylene, kerosene, diesel fuel, fuel oiland petroleum naptha. Such diluents can be employed in amounts rangingfrom zero to about 90 percent or more (weight basis) of the totalcomposition.

The compositions of the present invention are prepared by mixingtogether an O-pyridyl phosphate insecticide with a phthalate ester inproportions effective to prevent appreciable decomposition of saidO-pyridyl phosphate upon heating of the composition. Where the weightproportions of the phthalate ester to the total composition is fromabout 70 to about 99 percent or more, good thermal protection of theO-pyridyl phosphate ester is attained. The compositions of the presentinvention can be heated without the appreciable decomposition of theO-pyridyl phosphate that would otherwise occur upon heating of theO-pyridyl phosphate compound alone. It is contemplated the compositionsof the present invention can be heated from temperatures of about 160°C. to about 200° C. and still provide good thermal protection of theO-pyridyl phosphate.

Methods for carring out the present invention are performed by (a)mixing the O-pyridyl phosphate and the phthalate ester in proportionseffective to prevent appreciable decomposition of the O-pyridylphosphate upon heating of the mixture and (b) incorporating said mixtureinto a thermoplastic resin. Generally, the thermoplastic resin is heatedto temperatures which soften or liquefy the resin sufficiently to permitincorporation of the mixture containing the O-pyridyl phosphate into theresin. The proportions of the phthalate ester to the O-pyridyl phosphateare those hereinbefore described for the composition. A preferredO-pyridyl phosphate for performing the methods of the present inventionis chlorpyrifos. A preferred phthalate ester is dioctyl phthalate.Thermoplastic resins which are suitable for performing the methods ofthe present invention include polystyrene, acrylonitrile, methacrylateester, polyethylene and combinations thereof. A particularly preferredresin is polyvinyl chloride (PVC). The amount of O-pyridyl phosphatewhich may be incorporated into the plastic resin varies, depending inpart upon the solubility of the O-pyridyl phosphate in the thermoplasticresin. Generally, the O-pyridyl phosphate is present in the resin inproportions ranging from about 0.01 to about 25 percent by weight,preferably about 1 to about 2 percent.

In another embodiment of the present invention, a thermoplastic resin, astabilizer for the resin, and a phthalate ester as hereinbeforedescribed, are kneaded together. The mixture of the O-pyridyl phosphateand the phthalate ester is further kneaded into the kneadedthermoplastic resin. The kneaded thermoplastic resin containing theO-pyridyl phosphate is then cooled and pelleted into beads, pellets orpieces used to manufacture plastic articles. The O-pyridyl phosphates,phthalate esters and thermoplastic resins are similar to thosehereinabove described.

The following examples illustrate the present invention in a manner bywhich it can be practiced but, as such, should not be construed aslimitations upon the overall scope of the same.

EXAMPLE 1

Predetermined amounts of technical grade chlorpyrifos and dioctylphthalate were mixed to give solutions containing 0.0, 79.8, 90.1 and95.0 percent by weight of dioctyl phthalate. Separate solutions wereheated to temperatures of 140° C., 160° C., 180° C. or 200° C. forperiods of zero (0), 30, 60 or 90 minutes (min). The solutions wereanalyzed for the amount of chlorpyrifos remaining in the solution.Results of the analysis are provided in Table 1.

                  TABLE 1    ______________________________________    Thermal Stability of Chlorpyrifos    in Dioctyl Phthalate                      Percent Chlorpyrifos           Proportion of                      Remaining After             Dioctyl Phthalate    30    60   90    Temperature             in Percent   0 Min.  Min.  Min. Min.    ______________________________________    200° C.              0.0         100.0   80.9  53.6 25.4             79.8         100.0   96.0  81.7 60.9             90.1         100.0   96.1  90.1 86.1             95.0         100.0   99.4  95.4 93.6    180° C.              0.0         100.0   92.6  86.1 81.6             79.8         100.0   95.5  95.0 89.0             90.1         100.0   97.7  95.8 94.0             95.0         100.0   99.4  98.0 95.8    160° C.              0.0         100.0   99.5  95.9 92.7             95.0         100.0   99.2  98.6 96.0    140° C.              0.0         100.0   100.0 99.7 99.5             95.0         100.0   100.0 99.6 99.6    ______________________________________

EXAMPLE 2

Predetermined amounts of polyvinyl chloride resin, a stabilizer anddioctyl phthalate were kneaded together at a temperature of 200° C. Atest group of pellets were prepared by further kneading a solutioncontaning chlorpyrifos and dioctyl phthalate into the resin mixture inamounts calculated to bring the concentration of chlorpyrifos in theresin to 1.0 and 2.0 percent by weight. The resin was subsequentlypelleted. A second group of pellets as controls were similarly preparedbut without the use of dioctyl phthalate. Chlorpyrifos used was takenfrom a formulation of Lentrek® 40F insecticide, trademark of The DowChemical Company, Midland, Mich. Lentrek® 40F insecticide is aformulation of about 99 percent chlorpyrifos and about 1 percent inertingredients based on a weight basis. After pelleting, the finalconcentration of chlorpyrifos remaining in the pellets was determinedand are presented in Table 2.

                                      TABLE 2    __________________________________________________________________________    Thermal Stability of Chlorpyrifos    in Polyvinyl Chloride (PVC)    Calculated Percent                  Percent Concentration of                               Percent Concentration of    Concentration of                  Chlorpyrifos Found in                               Chlorpyrifos Found in    Chlorpyrifos in PVC                  PVC Without Use of                               PVC With the Use of    Immediately After Addition                  Dioctyl Phthalate                               Dioctyl Phthalate    __________________________________________________________________________    1.0           0.76         0.98    2.0           1.55         1.98    __________________________________________________________________________

What is claimed is:
 1. A composition consisting essentially of(a) anO-pyridyl phosphate compound of the formula ##STR4## wherein Rrepresents halopyridyl,Z is oxygen or sulfur, and each R¹ isloweralkoxy, amino or loweralkylamino; and (b) a phthalate ester of theformula ##STR5## wherein Y is alkyl from 2 to 20 carbon atoms or##STR6## wherein Y¹ is alkyl from 1 to 20 carbon atoms and Y² ishydrogen or methyl,said O-pyridyl phosphate and said phthalate esterbeing present in proportions effective to prevent appreciabledecomposition of said O-pyridyl phosphate upon heating said composition.2. The composition of claim 1 wherein said O-pyridyl phosphate ischlorpyrifos.
 3. The composition of claim 1 wherein said phthalate esteris dioctyl phthalate.
 4. The composition of claim 1 wherein saidO-pyridyl phosphate is chlorpyrifos and said phthalate ester is dioctylphthalate.
 5. The composition of claim 1 wherein the phthalate ester ispresent in the composition in proportions ranging from about 70 to about99 percent by weight.
 6. The composition of claim 5 wherein thephthalate ester is present in the composition in proportions rangingfrom about 90 to about 95 percent by weight.
 7. The composition of claim5 wherein the O-pyridyl phosphate is chlorpyrifos.
 8. The composition ofclaim 6 wherein the O-pyridyl phosphate is chlorpyrifos.
 9. Thecomposition of claim 5 wherein the phthalate ester is dioctyl phthalate.10. The composition of claim 6 wherein the phthalate ester is dioctylphthalate.